Golf club



June 8, 1937.

S. J. CROOKER GOLF CLUB Filed Aug. 15, 1956 15 their manufacture.

Patented June 8, 1937 UNITED STATES PATENT OFFICE 3 Claims.

My present invention relates to golf clubs, and more particularly to animproved shape of the golf club head which has the least possible airresistance, concentrates the weight behind the 5 striking point,provides greater playing accuracy,

and is simple to manufacture.

This invention is applicable to the so-called woods, but may also beapplied to golf club heads made from metals, or materials other thanwood. v

Heretofore, golf club heads of wood have been made with an off-set shankto which the shaft is attached, and have been made in various irregularshapes requiring expensive hand work in The ofi-set shank of the headresults in an unbalanced mass at the end of the shaft, and the customaryhead shapes have considerable air resistance even though the rearportions may be tapered in partial streamline contour.

When a player swings a .golf club at high speed to strike the ball, thetotal force exerted consists essentially of two parts; (a) the forcerequired to accelerate the mass of the club head, and (b) the forcerequired to overcome the resistance of the air, which increases as thesquare of the velocity of the club head.

Experiments indicate that any individual player is capable of puttingonly his own quota of energy into the swing of the club. If, therefore,the force (1)) required to overcome the resistance of the air can bereduced to a minimum, the player can utilize the difference to attain ahigher club head speed, which will result in a greater ball velocity anda longer drive.

Experiments have shown that an expert golfer can'swing a driver having a7 ounce, or 0.437 110., head to attain a head speed of 1'70 ft. per see.

As an example, if the distance over which the 40 club head travels fromthe position of rest back of the shoulder down to the point of contactwith the ball is assumed as 1'7 feet, the force (a) required toaccelerate this club head up to the stated velocity may be calculated byusing the formula:

where we represents the weight of the club head,

'Uc represents the velocity of the club head,

it. per sec.

g 'is the gravity factor=32.2 ft. per

sec. per sec.,

S is the distance of travel=17 ft.

The calculated force of acceleration (a) is therefore:

If the air resistance of the common type of off-set golf club head maybe expressed by the approximate formula:

R1=0.000005 A1902, lb.

Where, A1 is the exposed cross-sectional area of the club head at rightangles to its lineof motion, taken as 8 sq. in. from a well knowndriver; the force (b) required to overcome the air resistance is foundto be:

R1=0.000005(8) =l.16 1b.

Or the total force required to swing the club up to the velocity of 170ft. per sec. is the sum of,

While the force required to overcome the air resistance of the fastmoving club head may be only 10 to 15 per cent of that required toaccelerate the mass of the club head, it can be shown that a reductionof the air resistance force to about 3'per cent of the total, willresult in increasing the driving range of the club at least 10 yards.

Given in Report No. 291 of the National Advisory Committee forAeronautics, the results of experiments made on model airship hulls ofdiiferent relative lengths indicate that the minimum air resistance isoffered by the airship hull model which has a length twice its maximumdiameter, or the fineness ratio of length to diameter, L/D=2.

Selecting this minimum resistance spindle shape for the body of the golfclub head, such modifications have been made as are essential to makingit a practical tool for golfers, and yet retaining-the characteristicsof least possible air resistance.

Since it is customary to use persimmon wood for such golf club heads,the diameter of the head will be determined by the required finishedweight, by the density of the Wood, and bythe practical modificationsnecessary.

If a 7 ounce head is required, in my invention the maximum diameter willbe about 2% in. 50 giving an exposed cross-sectional area at the maximumdiameter of about 5 sq. in.

This golf club head may of course be weighted with suitable pieces oflead or other metal, and it may also be provided with a metal soleplate,

inset face plate, or other embellishment without altering the intent ofthe invention.

If the true streamline airship spindle shape results in a lowerresistance coefficient, the resistance offered by the air may beexpressed moderately by the equation:

And if it be assumed that the least attainable air resistance will nowpermit the player to increase the speed of the club head to 176 ft. persec., then the air resistance of the streamlined golf club spindle headwill be found to be about,

R2=0.0000025(5) (176) =0.388 lb.

or only about 3 per cent of the total; and the player will have a forceof 12.27 lb. available for accelerating the mass of the club head.

If the first given force equation is rearranged to solve for the clubhead velocity, the conditions of the example will give:

2gsF 64.4(17)12.27 w, 0.437

when struck by a club head of effective weight,

we, which is moving at the velocity, He, provided the elasticcoefficient of restitution of the ball, e,

3 is known. The equation is:

Experiments indicate that the elastic coefficient of the average golfball changes with the velocity of impact, being less at greatervelocities, ap-

proximately in accordance with the empirical equation:

If the standard 'golf ball has a weight of 1.62 ounces, and is struck bya 7 ounce club head, which is moving at 170 ft. per sec.; thecoeflicient of restitution, e, will be about 0.425; and the ball willleave the club head at a velocity of 197 ft.

per sec.

Therefore, if the same player can swing the spindle streamlined club atan increased speed of 176 ft. per sec., the corresponding elasticcoefficient of the ball will then be 0.412; and the ball, will beprojected at a higher velocity of 201 ft. per sec.

This increased ball velocity of 4 ft. per sec. may not seem large, butit can be shown by proper. ballistic calculations, assuming the ballsleave at an angle of departure of 15 degrees, and

with the back-spin rate of 7200 R. P. M., that the driving club of thecustomary style will give the ball a horizontal. free flight range ofonly 230 yards, while the improved spindle body streamlined driver willincrease the free flight range to 240 yards.

By the use of the spindle type streamlined driver, it happens to workout that this same rel- 70 ative increased distance will be added to thedrives of the amateur as well as to those of the expert golfer.

In my development in this art, I have discovered from aerodynamic,dynamic, geometric, and

75 practical considerations, that the usual ofi-set shank for attachingthe shaft to the head of the golf club is detrimental and shouldproperly be eliminated; and that the shaft may be inserted into orsecured directly to the main body of the spindle type streamlined golfclub head, thus improving its useful characteristics, and at the sametime greatly simplifying the manufacturing procedure.

Any suitable type of shaft may be used with this golf club, but themodern steel shaft having reasonable lateral flexibility and torsionalrigidity is preferred.

An object of my invention, therefore, is an improved golf club.

In the accompanying drawing illustrating a preferred embodiment of myinvention which may be employed in the manufacture thereof:

Figure 1 is a plan view of the golf club embodying my invention;

Figure 2 is a side elevation view, and Figure 3 is a front elevationView which maybe used in manufacturing a golf club according to myinvention.

Figure 4 shows the complete club.

Referring to the drawing, l designates the front striking face of theclub head, 2 and 3 represent respectively the forward and rearwardstreamline body curves, 4 represents the sole of the club head, 5 thehole or point of attachment for the shaft, 6 the grooves in the strikingface I, 1 the radius of curvature of body curve 2, and 8 the radius ofcurvature of body curve 3.

The basic shape of the improved golf club head may be called a spindle,being a solid of revolution generated by a plane area the bounding curveof which is revolved 360 degrees about a chord perpendicular to the axisof the curve.

While the generating curve of a spindle may be a segment of a circle, anellipse, a parabola, or other curve, for the purpose of describing myinvention the circular spindle will be considered suitable.

The basic streamline contour of the generating plane may beapproximately described by two radii defining the two revolving arcs orbody curves 2 and 3.

The forward arc 2 lying between the frontal point and the end of themaximum body diameter D may have a radius slightly larger than one-halfthe maximum diameter and will be centered on that transverse diameter.

The rearward are 3 lying between the end of the maximum diameter D andthe stern point of the longitudinal axis L will be described by a longradius 8 centered on the maxium diameter extended and passing throughthe end of the transverse diameter D and the stern point of L about twodiameters, 2D, from the frontal point.

This streamlined plane when revolved about the longitudinal axis L willdescribe a solid of revolution havingapproximately the required airshipstreamline bi-curvature spindle shape. This contour may however bealtered or modified in any practical manner without voiding the trueintent of my invention.

In effect the improved golf club head is formed by joining two halfspindles of different shapes defined by the rotation of two adjoiningportions of circular, elliptic, or other suitable plane segments aboutthe common chord axis.

Because it is necessary to slope the striking face of the club headbackward for the purpose of projecting the ball at an upward angle ofseveral degrees, the face of the driver usually has a. slope of about 10degrees, the brassie about 15 degrees,

and the spoon about 18 degrees. The nose of the streamlined body mustnecessarily be cut off at the proper angle and at a suitable-distanceback of the frontal point to provide a circular striking facehavingapproximately the same diameter as the golf ball.

Also for practical purposes the striking face must be low enough to hitunder the side of the ball and lift it out of the grass, therefore, itis necessary to cut off the lower portion of the body of the club headto provide a relatively flat horizontal sole 4.

To preserve aerodynamic qualities which means the least possible airresistance, the junctures between the surfaces 1 and 2, and between 4and the body of the club, are rounded off to smooth curves with ampleradii of curvature.

In order that a slight misalignment of the axis of the club head in thehorizontal plane at the instant of contact may not project the ball inan undesired direction, the striking face is slightly rounded or shapedinto cylindrical form with a radius of about 10 inches, the axis of thecylinder being parallel to the slope of the face and intersecting thelongitudinal axis of the club head.

Because the back-spin of the ball results in a long soaring flight it isdesirable to have the striking face furrowed with horizontal grooves 6,which gear to the ball surface and naturally give it back-spin. Verticalor cross-wise grooves are undesirable because if the club happens tohave a slight sidewise pull or push at the instant of contact, suchgrooves will tend to give the ball a partial side-wise spin resultingin' a hook or a permit side-wise slippage of the ball and minimize theslicing effects of a faulty stroke. 0

The shaft is preferably inserted or attached at an angle of about 50degrees from the horizontal plane and at a point slightly forward of andslightly below the normal center of gravity of the club head, in orderto preserve the proper hanging balance and feel in the swinging club.

This location of the shaft places its axis nearly in line behind thepoint of impact; the geometric shape of the head effectivelyconcentrates its weight behind the point of impact; and the streamlineshape of the head operates, to steer its direction more accurately whenapproaching contact with the ball. All factors taken together result toform a golf club which has been shown by test to be more accurate thanthe customary style of club, and with which the golfer is likely toobtain more consistent and satisfactory results. 55 This spindle type ofgolf club head in addition slice, whereas the horizontal grooves alonewillto being an improvement as a driver for the high speed strokesrequired in long driving, is ideal for shooting from grass lies, or forplaying out of the rough. While the usual brassie or spoon has a sharpleading edge extending 1 inches or more across the base of the strikingface, and usually cuts a swath of this width through the grass onapproaching the ball; the airship. spindle type streamline head asdescribed has a partially rounded nose which effectively parts the grasson approach to the ball and thus the grass offers much less resistanceto the motion of the club. This rounded nose club head will not betwisted and diverted by the work of cutting the grass, and will reachthe ball with a higher speed, which will result in a longer and moreaccurate shot than ameter and then tapers rearwardly, said head havingsubstantially streamline contours in all planes passing through thelongitudinal axis, the basic ratio of height to width being unity in allsections perpendicular to the longitudinal axis through the fore and afttapered contours of the club head, said head having its bottom side outhorizontally to provide a flat sole.

2. A golf club consisting of an elongated club -head of substantiallycircular cross-section throughout made with its length extending in theintended direction of its stroke, and tapering off to its stem end, thebottom side out horizontally to provide a flat sole, and bored angularlyforward of its center of gravity. in a plane at right angles to itslongitudinal axis, and of a shaft attached thereto.

3. A golf club consisting of an elongated club head of substantiallycircular cross-section throughout made with its length extending in theintended direction of its stroke and slightly narrowing from its maximumcross-section toward its striking face, and tapering oil to its stemend, the bottom side cut horizontally to provide a fiat sole, and boredangularly forward of its center of gravity in a plane at right angles toits longitudinal axis, and of a shaft attached thereto.

SYLVAN JAY CROOKER.

